The present invention relates to a system for attaching a flexible expansion joint to the surface of a building such as the floor or roof of a building. In particular, the system for attaching the joint is configured to secure the joint and provide, in effect, a form up to which a top coat of material such as concrete or asphalt can be applied over an existing structure. The system provides a universal base unit upon which common extension units can be attached and stacked to vary the height of the form for the surface coat.